[Mesa-dev] Adding support for sRGB framebuffers to EGL

[Brian Paul]

Just some quick comments.

I think the term "GAMMA" should be omitted.  I'm no expert but I'm not 
sure that sRGB is strictly a gamma function.  The GL_EXT_texture_sRGB 
spec says "The sRGB color space roughly corresponds to 2.2 gamma 
correction."  Also, the term GAMMA doesn't appear in any of the 
existing GLenum values related to sRGB.

Therefore, I think EGL_GAMMA_SRGB_BIT should be just EGL_SRGB_BIT,
EGL_GAMMA_LINEAR -> EGL_LINEAR,
EGL_GAMMA_SRGB -> EGL_SRGB.

For the query, you might use "COLOR_ENCODING" like 
GL_ARB_framebuffer_object.

You could also take a look at 
http://www.opengl.org/registry/specs/EXT/framebuffer_sRGB.txt to see 
how this was handled for GLX and WGL.

-Brian


On 09/26/2012 04:49 AM, John Kåre Alsaker wrote:
> EGL_GAMMA_SRGB_BIT should be changed to a boolean EGL config attribute
> so it can be optionally sorted by eglChooseConfig. It should be sorted
> after EGL_COLOR_BUFFER_TYPE and true values would be preferred. This
> sorting should be optional and is done so compositing window managers
> can sample the framebuffer as an sRGB texture. EGL_GAMMA_SRGB_BIT
> could also optionally be disabled when the format is not supported as
> an sRGB texture by the hardware.
>
> On Wed, Sep 26, 2012 at 10:19 AM, John Kåre Alsaker
> <john.kare.alsaker at gmail.com>  wrote:
>> The way this would interact with ARB_framebuffer_sRGB is that the
>> EGL's surface EGL_GAMMA attribute would be ignored. If a EGL config
>> has the EGL_GAMMA_SRGB_BIT, it is required to support sRGB for the
>> default OpenGL framebuffer.
>>
>> On Tue, Sep 25, 2012 at 5:58 PM, John Kåre Alsaker
>> <john.kare.alsaker at gmail.com>  wrote:
>>> Hello,
>>>
>>> I would like add support for sRGB framebuffers to EGL. Here are my
>>> proposed changes to EGL:
>>>
>>> A new EGL_SURFACE_TYPE bit:
>>> EGL_GAMMA_SRGB_BIT - This format supports sRGB framebuffers. This also
>>> means that ARB_framebuffer_sRGB is supported for this format.
>>>
>>> New values:
>>> EGL_GAMMA_LINEAR - The gamma is linear.
>>> EGL_GAMMA_SRGB - The gamma is as defined by the sRGB standard.
>>>
>>> New EGL surface attribute:
>>> EGL_GAMMA - The gamma of the surface's framebuffer. The default value
>>> is EGL_GAMMA_LINEAR.
>>>
>>> When the surface's EGL_GAMMA attribute's value is EGL_GAMMA_SRGB and
>>> this is supported by
>>> the format, reads from this framebuffer will be converted from sRGB
>>> gamma and writes will
>>> be converted to sRGB gamma. This may not apply to all functions in the
>>> client API.
>>>
>>> There may be something related to the ARB_framebuffer_sRGB extension
>>> in EGL already, in
>>> which case someone should link me to it.
>>>
>>> There's two assumptions behind this proposal. One is that you won't
>>> support sRGB only
>>> formats. The other is that linear gamma and sRGB gamma format support
>>> is the same.
>>> This means that window systems can't add a new linear gamma format
>>> without adding an sRGB
>>> format and the other way around.
>>>
>>> I'd like some comments on this proposal and tips on how it could be
>>> implemented in the
>>> mess that is DRI.
>>>
>>> Thanks,
>>> John Kåre
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